Apparatus and method for controlling registration

ABSTRACT

Control apparatus for controlling registration in a multistation printing system incorporates a phototransistor for producing a pulse in response to light impinging thereon, and a multistage amplifier capacitively coupled to the phototransistor for amplifying the pulse. The input of the amplifier is shortcircuited, except during short periods which overlap the pulses, so as to prevent faulty operation due to varying ambient conditions.

United States Patent 1 [111 3,899,686 Luska Aug. 12, 1975 [54] APPARATUS AND METHOD FOR -TJXLZIS l/l974 Penny 250/206 CONTROLLING REGISTRATION [75] Inventor: Zdenek Luska, Lausanne. Primary Examiner jame5 Lawrence Switzerland Assistant Examiner-Davis L. Willis I Attorney Agent, or FirmHill, Gross, Simpson, Van [73] Assigneez J. Bobst & Flls S.A., Switzerland santen Steadmzmv Chiara & Simpson [22] Filed: Oct. 17, 1973 [2]] Appl, No; 407,187 57 ABSTRACT Control apparatus for controlling registration in a mul- [30] Forelgn Appl'canon Pnonty Dam tistation printing system incorporates a phototransistor Oct. 27. I972 Switzerland 15713/72 for prod cing a pulse in response to light impinging thereon, and a multistage amplifier capacitively cout v t y 4 a a i i t /55 pied to the phototransistor for amplifying the pulse [5|] Int- Clj The input of the amplifier is short-circuited, except Field of Search 250/206. 555', 2 6/ 9 during short periods which overlap the pulses, so as to prevent faulty operation due to varying ambient con- [56] References Cited difi UNITED STATES PATENTS 3120,83? 3/1973 Clemens et a1. 250/206 3 Draw figures SHEEI PATENTED AUG 1 21975 SHEET APPARATUS AND METHOD FOR CONTROLLING REGISTRATION BACKGROUND 1. Field of the Invention The present invention relates to control apparatus and, more particularly, to control apparatus adapted to assist in obtaining proper registration in successive stations of a multi-station printing press or the like.

2. The Prior Art During a process involving multiple stations which must function in synchronism, for example, to print successive images in the same registration, it is necessary to provide a suitable regulating device for effecting the required registration. Well known examples of such registration devices are known in multicolor presses, in which the outlines of successive colors must register with the outline of previous colors so as to form the final image in correctly registered form. The required registration is generally obtained by employing data marks on the material which is being printed, the passage of the marks being detected by photosensitive devices. In order to identify the data marks, it is necessary to provide a means for distinguishing the marks from all other signals which may resemble them, such as unwanted specks of dirt, dust, and the like, and from interference resulting from background noise. When there is insufficient contrast in appearance between the background and the data mark, registration control systems are particularly subject to interference.

It is known to employ a window generating apparatus for allowing reading of the data mark only during predetermined periods, sometimes referred to as window periods. A system employing this technique is disclosed and claimed in my co-pending application, Ser. No. 339,926, filed Mar. 9, I973. While such systems are extremely useful under many circumstances, the method which they employ does not solve the problem of signal identification with respect to interfering signals, such as result from insufficient background contrast and the like.

In the present invention, background noise and ambient contrast effects are minimized by the use of a coupling capacitor which interconnects the photosensitive device with the control mechanism, so that changes in ambient conditions are represented primarily as changes in the charge on the capacitor, and are not manifested as signals presented to the control mechanism. Such a condenser is sometimes called a decoupling condenser," because it functions to decouple the input of the control mechanism from the photosensitive device.

However, the condenser also acts as a source of interference in connection with the reading of the data mark, since it retains, in the form of an electric charge, the signals which are received by the photosensitive device before the data mark is encountered. The effect of the charge on the condenser is to vary the initial voltage threshold at the time of reading the data mark to be detected. This variation in the voltage threshold renders it sometimes difficult to identify the data mark signal, and in some cases may result in suppression of the data mark signal.

It has been proposed to eliminate the errors described above by using several photosensitive devices, so as to take account of the background level against which the data mark appears. While such a system minimizes the effects of localized sources of noise, this system also can be upset by variations in the reading threshold level.

BRIEF SUMMARY OF THE INVENTION It is a principal object of the present invention to provide apparatus for assisting in registration between stations of a multistation operation, in which the effects of background noise and contrast variations are minimized.

Another object of the present invention is to provide a system and method for accomplishing the foregoing with a minimum of complexity and cost of construction.

These and other objects of the present invention will become manifest by an examination of the following description and the accompanying drawings.

In one embodiment of the present invention there is provided a phototransistor which is responsive to a change in light occurring in response to a data mark to produce a pulse corresponding to passage of the data mark through a predetermined location, an amplifier connected to a control mechanism for amplifying the pulse produced by the photosensitive device and supplying said pulse to the control mechanism, a capacitor interconnected between the photosensitive device and the amplifier, and means for shortcircuiting the input terminals of the amplifier except during predetermined time periods bracketing the time of occurrence of each of the pulses.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration of a system incorporating an illustrative embodiment of the present invention;

FIG. 2 is a circuit diagram of the apparatus illustrated in FIGv I; and

FIG. 3 is a circuit diagram of apparatus embodying the present invention, shown in more detail.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. I, a photoelectric cell 1 is interconnected by means of a condenser Cl and a coupling resistor R1 to the input of an amplifier 2. The amplifier is provided with a feedback resistor R2, selected to provide the appropriate gain for the amplifier 2 while insuring stability of operation. A switch 3 is provided for selectively grounding the junction between the capacitor C1 and the resistor R1, effectively shortcircuiting the input of the amplifier 2. The switch 3 is illustrated as connected by a control line 5 to a control unit 4.

Several structures implementing the arrangement of FIG. 1 may be designed. The switch 3 may be a cam operated switch, with the control unit 4 taking the form of a cam rotatable with a drive shaft of the multi-station machine, so that the switch 3 is open only at certain periods and is closed between such periods. These periods coincide with the so-called window periods" described in my co-pending application, Ser. No. 339,926, referred to above, and the disclosure of which is hereinto incorporated by reference.

Alternatively, the switch 3 may take the form of an electronic switch which is controlled electrically by means of a signal derived from a control until 4, responsive to each rotation of a drive shaft of the multistation system for producing a pulse or other control signal which functions to momentarily open the switch 3 during the window period. As such apparatus is described and claimed in my co-pending application, Ser. No. 339,926, it need not be described in detail herein.

The output of the amplifier 2 is connected to control apparatus (not shown) by which the registration of the multi-station system is regulated and controlled. Such apparatus may be, for example, the computing apparatus illustrated and claimed in a co-pending patent application of Roger-Henri Roch, Ser. No. 295,969, the disclosure of which is hereinto incorporated by reference.

A more detailed embodiment is illustrated in FIG. 2. A phototransistor TI is employed as the photosensitive element. Its collector is connected to a source of operating potential at a line 10, and its emitter is connected through a resistor R3 to a negative reference potential on a line 12. The emitter of the phototransistor TI is connected through the coupling capacitor C1 to the input of an amplifier incorporating three transistors, T2, T3, and T4. The transistors T2 and T3 are both connected in cascade in common emitter configuration, while the transistor T4 is connected as an emitterfollower amplifier. The collectors of the transistors T2 and T3 are connected to the line 10 by means of resistors R5 and R9, respectively. The emitter of the transistor T3 is connected by means of a line 14 to ground, while the emitter of the transistor T2 is connected by means of a resistor R6 to the line 12. The emitter of the transistor T4 is connected to the output line 16, and is also connected to the line 12 by means of a resistor R12.

A network including resistors R7 and R10 and acapacitor C2 is connected to furnish a feedback signal, derived at the emitter of the transistor T4, to the emitter of the transistor T2, to establish the gain of the multistage amplifier and to assure stable operation.

The switch 3 is interconnected between the base of the transistor T2, which forms the input stage of the three stage amplifier, and ground. When the switch 3 is open, the emitter of the phototransistor Tl produces a signal which passes through the condenser Cl and is developed across the input resistor R4, interconnected between the base of the transistor T2 and ground. When the switch 3 is closed, however, the input resistor R4 is short-circuited, with the result that the output 16 of the amplifier is maintained at a uniform level, indicative of the absence of a data mark pulse. During this interval, any variations in the voltage developed across the resistor R3 as a result of noise, changes in background contrast, and the like, affect the charge on the capacitor CI, but this charge does not change the potential at the input of the three stage amplifier, which is held at ground by the switch 3. During a window period, when the switch 3 is open, the capacitor Cl is 0perative to pass pulses from the phototransistor TI to the base of the transistor T2, so that a positive pulse is produced on the output line 16 in response to recognition of a data mark. Any variations in charge in the capacitor, however, which may accompany noise pulses developed by the phototransistor T1, are not manifested in changes in the input level applied to the amplifier.

In FIG. 3, a circuit embodying the present invention is shown in greater detail. In the circuit of FIG. 3, the

phototransistor T1 has its collector connected to the line 10 and its emitter connected through the resistor R3 to the line 11, which has a reference potential established thereon by virtue of a zener diode l8 and a resistor 20 interconnected between ground potential and the line 12, the line 12 being connected to a source of negative potential at a terminal 22. By this means, a certain negative potential, relative to ground, is established on the line 11. Instead of being coupled directly to the capacitor C1, the emitter of the phototransistor T1 is connected through an amplifying stage comprising a transistor T5 connected in emitter-follower configuration. The emitter of the transistor T1 is connected to the base of the transistor T5, and the emitter and the base of the transistor T5 are connected, respectively, through resistors R14 and R16 to the line 10 and to the terminal 22. An amplified signal is made available at the emitter of the transistor T5, and the emitter is connected through the capacitor C l to the base of the first stage transistor T2 of the three stage amplifier. The base of the transistor T2 is also connected to ground through the resistor R4.

The amplifier circuit incorporating the transistors T2, T3, and T4 is connected in substantially the same manner as illustrated in FIG. 2. A resistor R13 connects the collector of the transistor T4 to the line 10. The potential on the line 10 is derived by a circuit including a zener diode 24 and a resistor 26 connected between ground and a terminal 28 which is connected to a positive source of potential. As a result, the line 10, which is connected to the junction of the diode 24 and the resistor 26, is maintained at a constant positive potential relative to ground.

The switch 3 illustrated in FIG. 3 includes a set of contacts extending between lines 30 and 32. These contacts are equivalent to the contacts illustrated in FIGS. 1 and 2 and are normally closed, but are open during the window periods, when it is desired to read a data mark. Two terminals 34 and 36 are adapted to be connected across a source of potential, and complete an electrical circuit extending from the source through a relay coil 38 associated with the set of contacts and a cam-operated switch 40. The switch 40 is caused to change from its normally closed state to an open state by rotation of a cam 42, when a notched area 44 rotates into juxtaposition with the switch 40. This occurs during the window period as described above.

It will be appreciated that a variety of different forms of switches may be employed for executing the function of the switch 3, and it is also contemplated that a variety of different constructions of amplifiers may be employed with the present invention, other than the specific forms illustrated.

It is evident from the foregoing that the embodiments which have been illustrated and described above function to provide a relatively great amount of protection against faulty operation as a result of noise signals and variations in background contrast. It will be appreci ated that a variety of other modifications and changes may be made by those skilled in the art without departing from the essential features of novelty involved, which are intended to be defined and secured by the appended claims.

What is claimed is:

1. In a system for controlling registration in a multistage process comprising means for generating a pulse in response to detection of a data mark on a strip of material being processed by said multistage process, an amplifier for amplifying said pulse, a capacitor for interconnecting said pulse generator and said amplifier, and a selectively operable switch for normally shortcircuiting the input of said amplifier.

2. Apparatus according to claim 1, including means for periodically opening said switch at a time coinciding with the generation of said pulse.

3. Apparatus according to claim I, wherein said generating means comprises a photosensitive device adapted to produce a pulse in response to a data mark on said strip.

4. Apparatus according to claim 3, wherein said photosensitive device comprises a phototransistor.

5. Apparatus according to claim I, wherein said amplifier comprises a multistage amplifier, and feedback means interconnected between the input and output of said multistage amplifier.

6. Apparatus according to claim 1, including means for opening said switch periodically for establishing window periods coinciding with pulses generated in response to a plurality of data marks spaced along said strip.

7. Apparatus according to claim 6, including means for operating said switch in synchronism with the operation of said multistage process.

8. For use in a system for controlling registration in a multistage process, the method comprising the steps of spacing a plurality of data marks along the length of a strip of material being processed by said multistage process, generating pulses in response to the passage of said data marks through a predetermined location, providing an amplifier for amplifying said pulses, connecting said pulses through a capacitor to said amplifier, and shortcircuiting the input of said amplifier except during periodic times coinciding with the arrival of said data marks at said predetermined location.

9. The method according to claim 8, including the step of synchronizing said short-circuiting with the operation of said multistage process.

10. The method according to claim 9, including the step of providing means operable in synchronism with said multistage process for periodically opening a normally closed switch connected across the input terminals of said amplifier. 

1. In a system for controlling registration in a multistage process comprising means for generating a pulse in response to detection of a data mark on a strip of material being processed by said multistage process, an amplifier for amplifying said pulse, a capacitor for interconnecting said pulse generator and said amplifier, and a selectively operable switch for normally shortcircuiting the input of said amplifier.
 2. Apparatus according to claim 1, including means for periodically opening said switch at a time coinciding with the generation of said pulse.
 3. Apparatus according to claim 1, wherein said generating means comprises a photosensitive device adapted to produce a pulse in response to a data mark on said strip.
 4. Apparatus according to claim 3, wherein said photosensitive device comprises a phototransistor.
 5. Apparatus according to claim 1, wherein said amplifier comprises a multistage amplifier, and feedback means interconnected between the input and output of said multistage amplifier.
 6. Apparatus according to claim 1, including means for opening said switch periodically for establishing window periods coinciding with pulses generated in response to a plurality of data marks spaced along said strip.
 7. Apparatus according to claim 6, including means for operating said switch in synchronism with the operation of said multistage process.
 8. For use in a system for controlling registration in a multistage process, the method comprising the steps of spacing a plurality of data marks along the length of a strip of material being processed by said multistage process, generating pulses in response to the passage of said data marks through a preDetermined location, providing an amplifier for amplifying said pulses, connecting said pulses through a capacitor to said amplifier, and shortcircuiting the input of said amplifier except during periodic times coinciding with the arrival of said data marks at said predetermined location.
 9. The method according to claim 8, including the step of synchronizing said short-circuiting with the operation of said multistage process.
 10. The method according to claim 9, including the step of providing means operable in synchronism with said multistage process for periodically opening a normally closed switch connected across the input terminals of said amplifier. 